Crack-resistant thermal bend actuator

Abstract

A thermal bend actuator comprises an active beam for connection to drive circuitry and a passive beam mechanically cooperating with the active beam. When a current is passed through the active beam, the active beam expands relative to the passive beam resulting in bending of the actuator. The passive beam comprises a first layer comprised of silicon nitride and a second layer comprised of silicon dioxide. The second layer is sandwiched between the first layer and the active beam to provide thermal insulation for the first layer.

Description

FIELD OF THE INVENTION [0001]The present invention relates to the field of MEMS devices and particularly inkjet printheads. It has been developed primarily to improve the robustness of thermal bend actuators, both during MEMS fabrication and during operation.CROSS REFERENCES [0002]The following patents or patent applications filed by the applicant or assignee of the present invention are hereby incorporated by cross-reference.7,416,2806,902,2556,623,1016,406,1296,505,9166,457,8096,550,8956,457,81220080129793-A120080129793-A120080129784-A120080225076-A120080225077-A120080225078-A12009013996112 / 323,47112 / 508,5642008030972812 / 114,82612 / 239,81412 / 142,779[0003]The disclosures of these co-pending applications are incorporated herein by reference.BACKGROUND OF THE INVENTION [0004]The present Applicant has described previously a plethora of MEMS inkjet nozzles using thermal bend actuation. Thermal bend actuation generally means bend movement generated by thermal expansion of one material, h...

AI Technical Summary

Benefits of technology

[0013]The thermal bend actuator according to the present invention is advantageously robust and resistant to cracking whilst maintaining excellent thermal efficiency. The first layer of silicon nitride provides the crack-resistance whilst the second layer of silicon dioxide provides thermal insulation, which maintains a high overall efficiency. Cracking may be problematic in thermal bend actuators due to inevitable stresses in the active and passive beams, but especially the passive beam which is usually formed from silicon dioxide having good thermally insulating properties. The present invention addresses the problem of cracking by using the bilayered passive beam described herein.

[0028]In addition to the advantages discussed above in respect of the first aspect, a further advantage of inkjet nozzle assemblies according to the second aspect is that the second layer of silicon nitride is an impermeable barrier to the fluid contained in the nozzle chamber. Accordingly, aqueous ions are unable to leach through the passive beam and contaminate the active beam, which may result in nozzle failure. Leaching of aqueous ions from hot ink has been identified by the present Applicants as a failure mechanism for thermal bend actuators having a passive beam comprised of silicon dioxide only.

Problems solved by technology

Cracking may be problematic in thermal bend actuators due to inevitable stresses in the active and passive beams, but especially the passive beam which is usually formed from silicon dioxide having good thermally insulating properties.

Images